Given a list of thousands of IPv4 addresses and that you have no direct access to these hosts, is there a service or a methodology to infer a subnet that's possibly being used?

  • no direct access to these hosts then it's not a network you manage, and therefore off topic. – Ricky Jul 22 '20 at 3:01

No. You can’t infer the subnet from the IP address alone.

  • The best one can hope for is to find the block to which the address belongs via WHOIS. But that won't tell you a LAN netmask. – Ricky Jul 22 '20 at 3:03
  • @RickyBeam Another source would be the ASN table but that's likely even less granular than Whois. – Zac67 Jul 22 '20 at 6:20
  • @Zac67 and the way people "protect" their address space, BGP will show everything as a /24. – Ricky Jul 22 '20 at 8:57

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